Showing papers on "Ring laser published in 2020"

Heterogeneous III-V on silicon nitride amplifiers and lasers via microtransfer printing

Abstract: The development of ultralow-loss silicon-nitride-based waveguide platforms has enabled the realization of integrated optical filters with unprecedented performance. Such passive circuits, when combined with phase modulators and low-noise lasers, have the potential to improve the current state of the art of the most critical components in coherent communications, beam steering, and microwave photonics applications. However, the large refractive index difference between silicon nitride and common III-V gain materials in the telecom wavelength range hampers the integration of electrically pumped III-V semiconductor lasers on a silicon nitride waveguide chip. Here, we present an approach to overcome this refractive index mismatch by using an intermediate layer of hydrogenated amorphous silicon, followed by the microtransfer printing of a prefabricated III-V semiconductor optical amplifier. Following this approach, we demonstrate a heterogeneously integrated semiconductor optical amplifier on a silicon nitride waveguide circuit with up to 14 dB gain and a saturation power of 8 mW. We further demonstrate a heterogeneously integrated ring laser on a silicon nitride circuit operating around 1550 nm. This heterogeneous integration approach would not be limited to silicon-nitride-based platforms: it can be used advantageously for any waveguide platform with low-refractive-index waveguide materials such as lithium niobate.

Characterization and experimental verification of actively mode-locked erbium doped fiber laser utilizing ring cavity

Abstract: Abstract A simple active mode-locked erbium-doped fiber (EDF) ring laser is characterized and experimentally demonstrated. The active mode-locked laser can be tuned in the C-band wavelength range 1525 nm to 1565 nm using a tunable bandpass filter placed in the cavity. An intensity modulator placed inside the laser cavity is driven using a sinusoidal signal at different repetition rates. The laser can produce trains of pulses with a width that is controlled using the mode-locking order. The experiments demonstrated an active mode-locked laser that can generate pulse trains with 39 ns width at multiple cavity fundamental frequency of 0.67 MHz repetition rate. Numerical simulations are conducted to investigate the effect of the tunable filter bandwidth and the power of the EDF 980 nm pump on the mode-locking process and produced pulses width.

Real-time observation of the optical Sagnac effect in ultrafast bidirectional fibre lasers

Abstract: The optical Sagnac effect sets fundamentals of the operating principle for ring laser and fiber optic gyroscopes, which are preferred instruments for inertial guidance systems, seismology, and geodesy. Operating at both high bias stability and angular velocity resolutions demands special precautions like dithering or multimode operation to eliminate frequency lock-in or similar effects introduced due to synchronization of counterpropagating channels. Recently, to circumvent these limitations, ultrashort pulsed radiation was suggested to supersede conventional continuous wave operation. Despite the ultrafast nature of ultrashort pulse generation, the interrogation of the Sagnac effect relies on highly averaging measurement methods. Here, we demonstrate the novel approach to the optical Sagnac effect visualization by applying real-time spatio-temporal intensity processing and time-resolved spectral domain measurements of ultrashort pulse dynamics in rotating the bidirectional ring fiber laser cavity. Our results reveal the high potential of application of novel methods of optical Sagnac effect measurements, allowing enhancement of rotation sensitivity and resolution by several orders of magnitude.

EDF ring laser using cascaded-chirped long period fiber grating for temperature measurement.

Abstract: A novel tunable erbium-doped fiber ring laser (EDFRL) using a cascaded-chirped long period fiber grating (C-CLPG) as a wavelength selection element is proposed. The oscillation wavelength is determined by the one of the spectral peaks of the C-CLPG used, and the oscillation output provides a high signal to noise (S/N) ratio detection and a highly sensitive measurement of the temperature due to its high power and narrow spectral output. In the experiment, it is confirmed that the wavelength of the output shifts in accordance with the temperature-induced spectral shift of the C-CLPG transmittance spectrum and the temperature sensitivity is obtained to be ∼-0.2 nm/°C within the wavelength range of 1567.30 ∼ 1575.78 nm. The oscillation wavelength range is to be limited depending on the fringe spacing of the channeled spectrum of C-CLPG, which limits the temperature measurement range, but a data processing approach to solve this problem is additionally proposed and its availability is also presented.

Room-Temperature Power-Stabilized Narrow-Linewidth Tunable Erbium-Doped Fiber Ring Laser Based on Cascaded Mach-Zehnder Interferometers With Different Free Spectral Range for Strain Sensing

Abstract: An automatically power-stabilized (with power fluctuation <0.155 dB), narrow-linewidth (0.0171 nm), wavelength-tunable (10.69 nm) erbium-doped fiber laser has been proposed by cascading two fiber Mach–Zehnder interferometers (MZI) without using any temperature controlling device. One of the MZIs (here called the 1st MZI) is composed of two 3 dB couplers to form interference patterns while the other MZI (here termed the 2nd MZI) is constructed with a tapered seven-core fiber (SCF) and based on the principle of supermode interference. For the two MZIs, the free spectral range (FSR), the passband bandwidth and the extinction ratio (ER) at 1560 nm are 0.37 nm, 0.19 nm, 16.6 dB and 13.93 nm, 7.93 nm, 10.1 dB, respectively. Due to the major difference between the two FSR values, the 1st MZI and the 2nd MZI respectively play a role in controlling the laser linewidth and suppressing the homogeneous broadening effect to reach to a satisfactory level of power stability. The 2nd MZI is also used to fine tune the laser wavelength by applying strain to the tapered SCF (TSCF) over the spectral range of 1570.22–1559.33 nm, with an incremental step of 0.37 nm being used. The side-mode suppression ratio (SMSR) of the tunable fiber laser can be up to 45 dB. By appropriately adjusting the polarization controller, dual wavelength lasing can also be achieved. For single wavelength lasing, the 3 dB laser linewidth is 0.0171 nm. The power fluctuation, without a temperature controlling device being used and operating at room temperature, is found to be less than 0.155 dB over 1 hour while the central wavelength drift is less than 0.19 nm.

Stabilization of passive harmonic mode locking in a fiber ring laser

Abstract: We propose the model of a harmonically mode-locked soliton fiber ring laser based on the nonlinear polarization rotation taking into account the gain depletion and recovery effects. It is shown that a specific timing jitter could arise in such lasers, since the pulses in the cavity are not strongly identical. To suppress the jitter and stabilize the harmonic mode-locking operation, a method using a small frequency shift followed by the laser radiation filtering is described. The performed numerical simulation shows that the proposed method is able to provide extremely stable harmonic mode locking in a soliton fiber ring laser.

Widely tunable erbium doped fiber ring laser based on loop and double-pass EDFA design

Abstract: This study presents two novel tunable erbium doped fiber ring laser (EDFRL) configurations based on loop EDFA design and double-pass EDFA design, respectively to achieve an ultra-wideband tuning range and stable single-longitudinal-mode lasing operation. A micro-electro-mechanical system (MEMS) based optical tunable band pass filter was utilized as the wavelength selection element. Output spectral and power characteristics of these EDFRLs were experimentally analyzed and discussed. The EDFRLs had moderate and stable output power level ( ~ -3 dBm) over 70 nm tuning range that covers C+L band. Moreover, the proposed EDFRLs could also suppress the undesired multi-longitudinal-modes successfully and have a high ( ~ 60 dB) OSNR level in whole tuning range.

Temporal cavity solitons in a delayed model of a dispersive cavity ring laser

Abstract: Nonlinear localised structures appear as solitary states in systems with multistability and hysteresis. In particular, localised structures of light known as temporal cavity solitons were observed recently experimentally in driven Kerr-cavities operating in the anomalous dispersion regime when one of the two bistable spatially homogeneous steady states exhibits a modulational instability. We use a distributed delay system to study theoretically the formation of temporal cavity solitons in an optically injected ring semiconductor-based fiber laser, and propose an approach to derive reduced delay-differential equation models taking into account the dispersion of the intracavity fiber delay line. Using these equations we perform the stability and bifurcation analysis of injection-locked continuous wave states and temporal cavity solitons.

Observation of PT-symmetry in a fiber ring laser.

Abstract: A wavelength-tunable single-mode laser with a sub-kilohertz linewidth based on parity-time (PT)-symmetry is proposed and experimentally demonstrated. The proposed PT-symmetric laser is implemented based on a hybrid use of an optical fiber loop and a thermally tunable integrated microdisk resonator (MDR). The MDR, implemented based on the silicon-on-insulator, operates with the optical fiber loop to form two mutually coupled cavities with an identical geometry. By controlling two light waves passing through the two cavities, with one having a gain coefficient and the other a loss coefficient but with an identical magnitude, a PT-symmetric laser is implemented. Thanks to an ultranarrow passband of the cavity due to PT-symmetry, single-longitudinal mode lasing is achieved. The tuning of the wavelength is implemented by thermally tuning the MDR. The proposed PT-symmetric laser is demonstrated experimentally. Single-longitudinal mode lasing at a wavelength of around 1555 nm with a sub-kilohertz linewidth of 433 Hz is implemented. The lasing wavelength is continuously tunable from 1555.135 to 1555.887 nm with a tuning slope of 75.24 pm/°C.

Evaluation of hot cracking susceptibility on laser welded aluminum alloy using coaxially arranged multiple-beam laser

Abstract: Dual-beam laser welding using an adjustable ring mode (ARM) fiber laser was implemented to evaluate weld bead characteristics and hot cracking susceptibility. An ARM laser with dual beams having diameters of 175 and 450 μm was implemented in the focal position. By controlling the core laser power (700–1800 W) and ring laser power (0–1100 W), respectively, full penetration welds were achieved for a 1 mm-thick Al 6014-T4 alloy even at a high welding speed of 120 mm/s under a total laser power of 1800 W. High welding speed enabled a small molten area and a narrow equiaxed dendrite structure along the bead center, which reduced hot cracking susceptibility.

Investigating single-longitudinal-mode operation of a continuous wave second Stokes diamond Raman ring laser.

Abstract: We report a diamond Raman ring cavity laser resonantly pumped by a tunable Ti:sapphire continuous wave laser. We characterize the laser operation generating first Stokes output and, for the first time, generate second Stokes lasing at a maximum output power of 364 mW with 33.4% slope efficiency at 1101.3 nm. Single longitudinal mode operation is achieved for all first Stokes output powers, but only for lower output powers for second Stokes operation. We discuss possible reasons preventing single longitudinal mode operation.

An Erbium Fiber Laser With Single-Frequency Oscillation and Wavelength-Upconverted Output

Abstract: In this paper, we present experimentally an erbium-doped fiber (EDF) laser system to accomplish the single-longitudinal-mode (SLM) and wavelength-upconverted output by using nonlinear effect. To accomplish the SLM output, a short length of unpumped EDF saturable absorber (SA) is applied inside the EDF laser cavity for filtering densely multi-mode noise. In accordance with the designed EDF laser system, the lasing wavelength can be upconverted to a longer wavelength position. In addition, the output characteristics of output power, optical signal to noise ratio (OSNR), tunability, stability and linewidth in the EDF laser are also discussed.

Graphene Capacitor-Based Electrical Switching of Mode-Locking in All-Fiberized Femtosecond Lasers.

Abstract: Effective high-capacity data management necessitates the use of ultrafast fiber lasers with mode-locking-based femtosecond pulse generation. We suggest a simple but highly efficient structure of a graphene saturable absorber in the form of a graphene/poly(methyl methacrylate) (PMMA)/graphene capacitor and demonstrate the generation of ultrashort pulses by passive mode-locking in a fiber ring laser cavity, with simultaneous electrical switching (on/off) of the mode-locking operation. The voltage applied to the capacitor shifts the Fermi level of the graphene layers, thereby controlling their nonlinear light absorption, which is directly correlated with mode-locking. The flexible PMMA layer used for graphene transfer also acts as a dielectric layer to realize a very simple but effective capacitor structure. By employing the graphene capacitor on the polished surface of a D-shaped fiber, we demonstrate the switching of the mode-locking operation reversibly from the femtosecond pulse regime to a continuous wave regime of the ring laser with an extinction ratio of 70.4 dB.

Tunable C-band and L-band multi-wavelength erbium-doped fiber ring laser based on a triple-core photonic crystal fiber with polarization-dependent loss

Abstract: A tunable C-band and L-band multi-wavelength erbium-doped fiber laser (MW-EDFL) based on a novel fiber filter is proposed and experimentally demonstrated. The fiber filter is composed of a segment of triple-core photonic crystal fiber (TCPCF) and a segment of multi-mode fiber (MMF) between single mode fibers, which is inserted into the ring cavity of MW-EDFL as tuning component and wavelength selector. Based on the axial strain response of fiber filter, a tunable single-, dual- and triple-wavelength laser can be obtained with the tunable range of 19.58 nm, 10.34 nm, 6.84 nm, respectively. Meanwhile, the side-mode suppression ratio of lasing output is higher than 50 dB and the 3 dB linewidth is 0.026 nm for single wavelength lasing. Moreover, the lasing outputs are proved to be very stable at room temperature with the maximum wavelength shift of 0.06 nm and power fluctuation of 0.96 dB. Such a MW-EDFL with relatively simple structure and easy preparation has wide applications in important fields such as medicine, military, communication, and sensing.

Polarization-Color Domain Walls in Fiber Ring Lasers

Abstract: The generation of dual-wavelength polarization-color domains (PCD) in a fiber ring laser is experimentally demonstrated. Wavelength-resolved measurements validate the existence of color domains (CD). Simultaneously, polarization-resolved measurements confirm the existence of polarization domain walls. The formation of PCD is attributed to cross-gain saturation combined with cross-polarization coupling through optical Kerr effect induced by the high nonlinear fiber.

Compact Tunable DBR/Ring Laser Module Integrated with Extremely-high-Δ PLC Wavelength Locker

Abstract: A compact tunable laser module integrating a newly developed DBR/Ring laser and an extremely-high-Δ PLC wavelength locker is demonstrated with narrow spectral linewidth of <100 kHz across the full C-band.

Sagnac Gyroscopes and the GINGER Project

Abstract: Large frame optical Sagnac gyroscopes, more commonly called ring laser gyroscopes, are considered the only device able to provide fast and very high sensitivity measurement of the length of the day (LOD), and of the Earth rotation axis variations. Several large frame Sagnac gyros are presently operative with high duty cycle and sensitivity well below fractions of nrad/s in 1 second measurement. At present other inertial angular rotation sensors are not competitive with ring laser gyroscopes. The feasibility depends on the so called hetero-lithic ring lasers. The present status of art is reported, and the feasibility of the main goals for geodesy discussed.

Multibound Soliton Formation in an Erbium-Doped Ring Laser With a Highly Nonlinear Resonator

Abstract: We have studied the generation of low-noise ultrashort multibound solitons in the telecommunication spectral window in an erbium-doped all-fiber ring laser with a highly-nonlinear resonator mode-locked by a nonlinear polarization evolution effect. The multibound soliton generation is obtained with more than 20 bound dechirped pulses with a duration of ~ 240 fs at a repetition rate of ~ 11.3 MHz (with a signal-to-noise ratio of ~ 73.3 dB), the relative intensity noise is $\sim 1.3\cdot 10^{\mathbf {-8}}$ with a time averaging window of ~ 100 s.

Continuous-Wave and Pulsed Operation of a Ring Laser Cavity with The Ho:YLF and Ho:YAG Crystals

Abstract: We demonstrate a 2.5 m ring laser with the Ho:YAG and Ho:YLF crystals end-pumped by the Tmdoped fiber laser. In the Ho:YAG laser, the continuous-wave (CW) output power was 4.72 W at a wavelength of 2090.8 nm when the incident pump power was 21.5 W, which corresponded to a slope efficiency of 26.3%. For the Q-switched operation with the 100 Hz pulse repetition frequency (PRF), an output energy of 5.16 mJ and a pulse width of 125.6 ns were achieved at a pump power of 9.53 W. In the Ho:YLF laser, up to a 4.14 CW output power was realized under an incident pump power of 22.3 W, which corresponded to a slope efficiency of 27.3%. At the 100 Hz Q-switched operation, the output energy was 4 mJ and the corresponding pulse width was 165.4 ns, when the pump power was 9.86 W.

Electro-Optic Tuning of a Monolithically Integrated Widely Tuneable InP Laser With Free-Running and Stabilized Operation

Abstract: We report on the free-running and frequency stabilized operation of a ring resonator-tuned full-band tuneable laser. The laser is a monolithically integrated semiconductor ring laser tuneable over 34 nm, from 1522–1556 nm, fabricated using a commercially-available, InP-based, active-passive foundry technology. The mode selection is implemented using the Vernier effect by reverse-biasing voltage-controlled electro-optically tuned ring resonators. The laser exhibits a typical intrinsic linewidth of 110 kHz over the C-band and a side-mode suppression ratio (SMSR) exceeding 50 dB. The linewidth over the tuning range does not significantly vary, showing that the tuning mechanism does not cause linewidth broadening. The power dissipated in the tuning elements is 1.4 mW per ring. Using the same reverse bias voltage-controlled electro-optic tuning, we also demonstrate the locking of the laser to a high-finesse etalon using Poun–Drever–Hall frequency locking. Our implementation requires a single control loop because of the reverse bias tuning. All deployed tuning effects in the phase modulators have the same sign therefore resulting in a flatter frequency dependent phase response compared to current injection feedback. The control loop has a bandwidth of 500 kHz and a control range of 2.9 GHz. We report 1 kHz level linewidth for millisecond observation times for the stabilized laser.

Multiplexed dynamic strain sensing system based on a fiber ring laser using a non-tunable fiber Fabry-Perot filter.

Abstract: In this paper, a non-tunable fiber Fabry-Perot filter (FFPF) is configured to demodulate dynamic strain signals in a multiplexed dynamic sensing system based on a fiber ring laser. A semiconductor optical amplifier (SOA) contained in the fiber ring laser cavity enables this system to implement multiplex operation because of the inhomogeneous broadening of the SOA source. The shift of the reflective spectrum of the fiber Bragg grating caused by external dynamic strain is demodulated by the FFPF in the laser cavity, which ultimately generates an amplified output. In the experiment, the sensing system can respond to dynamic strains at ultra-high frequencies up to megahertz, and an example for detection of ultrasonic signals in water has been successfully demonstrated. A dual-channel system for multiplexing demodulation is also discussed. This system presented here has a simple structure and a low cost, which makes it attractive for dynamic strain detection in structural health monitoring.

Feedback-Injected Erbium Fiber Laser With Selectable Tunability and Constant Single-Longitudinal-Mode Characteristic

Abstract: In this investigation, a wavelength-selected single-longitudinal-mode (SLM) erbium-doped fiber (EDF) ring laser utilizing C-band EDF based gain medium over a tuning bandwidth of 1524.0 to 1573.0 nm is demonstrated experimentally. A self-injection Rayleigh backscattering (RB) is designed in the EDF ring laser configuration to suppress the multi-longitudinal-mode (MLM) oscillation and narrow the obtained linewidth. Here, the physical output features of the proposed self-injected RB EDF laser are also studied and discussed, such as the optical signal to noise ratio (OSNR), output power, and laser linewidth, respectively. Therefore, the demonstrated EDF laser not only can reach SLM output, but also can produce a flat output spectrum of 1524.0 to 1554.0 nm with 0.2 dB power variation. Moreover, the measured fluctuation of each wavelength can be kept at ±0.05 nm based on the presented self-injected RB EDF laser, while the uncertainty issue is also considered.

Geometry optimization of unidirectional integrated ring laser

Abstract: Ring lasers, evanescently coupled to an adjacent optical waveguide, are essential components for the upcoming generation of integrated sources. In an ideally symmetric resonator, emission occurs from the both clockwise and counter-clockwise directions, resulting in a potential waste of emitted optical power, while unidirectional emission has been reported in different configurations, for example when asymmetric external reflectivities are used for the coupling waveguide. In the integrated form, a common approach consists in the inserting an S-bend waveguide in the ring, in such a way that the field propagating in the direction that we want to suppress is reinjected in the other direction. The S-bend waveguide must be carefully designed to reduce optical losses and to ensure a sufficient suppression of the undesired field. Using 2D finite- difference time-domain simulations performed with Synopsys RSoft©, we report a systematic analysis of the racetrack geometry of a 86.8 μm long microring laser including an inner S-waveguide, and we maximize the unidirectionality of the ring laser, scanning the gap distance between external racetrack resonator and S-bend waveguide. The results of this numerical analysis can be finally used to generate the mask layout of the improved unidirectional ring laser, targeting a Process Design Kit of choice, taking advance of the integration of RSoft with the software OptoDesigner.©

Measurement of optical homogeneity of ZnGeP 2 crystal using a 2.02 µm single-longitudinal-mode Tm:LuAG ring laser

Abstract: We demonstrate a single-longitudinal-mode Tm:LuAG unidirectional ring laser based on the Faraday effect and its application in measuring the optical homogeneity of ZnGeP2 (ZGP) crystal. The maximum single-longitudinal-mode power was 511 mW at 2022.4 nm, with a slope efficiency of 9.7%, and the M2 factors were 1.13 and 1.23 in the x and y directions, respectively. The laser was s polarized with a polarization degree of 30 dB. Also, the optical homogeneity of ZGP crystal was measured by the Mach-Zehnder interference method, which adopts the single-longitudinal-mode laser as the monochrome source. According to the interference fringes, the quantitative calculation or qualitative analysis of the optical homogeneity of ZGP crystal was achieved, which could quickly and conveniently judge the quality of ZGP crystal, and provided high-quality crystals for high-power mid-infrared lasers. To our knowledge, it is the first report of the optical homogeneity measurement of ZGP crystal by a 2 µm single-longitudinal-mode laser.

Effect of Unequal Intensities of Counter-Propagating Waves on the Frequency Response of Laser Gyroscopes

Abstract: Frequency response of a laser gyroscope was studied by numerical modeling of a complete system of equations describing it. The calculation results are compared to the results of experimental measurements taken on a precision dynamic test bench. The frequency response was measured for a gyroscope based on a four-mirror ring laser with a non-planar contour, operating on He–Ne active mix at the wavelength of 632.8 nm. In the gyroscope under study, the sign-variable dither was implemented on the basis of Zeeman magnetooptical effect. The relationship between the measured and designed values of the frequency response distortions has been found. The relationship between the frequency response distortions in a laser gyroscope and inequality of field intensities of the counter-propagating waves (CPW) has been numerically calculated and confirmed by experiments. Based on the research results, the parameters of a ring laser can be optimized to improve the accuracy of measurements by means of laser gyroscopes.